How the Test Will Feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the Test is Performed

The test is usually done for patients who are severely ill with acute kidney insufficiency. The test helps determine if the drop in urine production is due to reduced blood flow to the kidney or to kidney damage itself.

What Abnormal Results Mean

A meaningful interpretation of the test can be made only when your urine volume has dropped to less than 500 mL/day.

A FENa of less than 1% indicates decreased blood flow to the kidney, while a FENa greater than 1% (and usually greater than 3%) suggests kidney damage.